There are four main elemental attacks in Diablo II: Fire, Cold, Lightning, and Poison. Each class can resist, or reduce
damage from, these attacks by using items or skills.

Curses and Bone-based attacks are not considered elemental, so these resistances will not protect against them.

Some monsters possess the ability to resist physical attacks and
magical damage as well as elemental damage. Monsters that can resist
magical attacks can also resist the Necromancer Bone spells
(Teeth/Bone Spear/Bone Spirit) and the Barbarian's Berserk.

Certain Unique monsters have Spectral Hit, which adds a random elemental property to every blow.

When to Use Resistances
Melee characters should consider wearing resistance-providing equipment at all times, as they are the least likely to avoid
elemental attacks. Ranged characters might wish to keep a set of "resistance gear" in your Backpack, Horadric Cube, or Stash. When you run into trouble
with monsters, put on your gear until the battle is over. Jewelry is best suited to this, as it only takes up a 1x1
space in your inventory. Depending on your character class, you may wish to keep a shield with high resistances in your
alternate Weapon Tab. You can switch to this shield when facing monsters with deadly elemental attacks. Charms also
work very well for adding additional resistances, especially "Resist All" Charms. As you play later Acts and
higher difficulties, Resistances will become very important. You may find that in Hell Difficulty you'll
have a difficult time surviving without a lot of resistances.

Ranged vs Melee Characters
Resistances are very important for melee, or hand-to-hand combat, characters. When fighting against monsters that have
ranged elemental attacks, they can side step or dodge, but not always. Characters using melee weapons have to close in on a
monster to kill it, exposing them to more elemental attacks. Resistances will reduce the amount of damage they take,
allowing them to fight longer, survive otherwise impossible battles, and waste fewer Healing Potions. Some elemental
attacks are difficult to avoid, such as those used by Undead Horrors, Willowisps, Unique monsters, and Bosses. In
these situations, even fighters with ranged attacks may want to improve their resistances.

Minimum Resistance

Your base resistance levels are determined by the game's difficulty:

Normal Difficulty: 0
Nightmare Difficulty: -40
Hell Difficulty: -100

The absolute minimum resistance is -100%. Resistance can never
be lowered to below that value.

The Scroll of Resistance increases your base resistance level with 10
per use. Note that if you die this bonus will disappear until you join
a new game. The Character Screen does not show this bug. For obvious
reasons this is only a concern to Softcore Characters.

Maximum Resistance
Each character has a default maximum resistance of 75%, although
certain items can raise that number as high as 95%. You can never
become totally immune to elemental attacks with Resistances
alone.

Lightning Resistance
Lightning Resistance comes in most handy against Lightning-Enchanted
Unique monsters. Each time you hit a Unique Lightning monster, it will
release a Charged Bolt to each of the four corners of the
screen. The more you hit the monster, the more Charged Bolts it
releases. High Lightning Resistance may save you in these situations.

Willowisps often attack with focused beams of lightning, much
like the Sorceress's Level 12 Lightning spell, albeit often more
powerful. Packs of these monsters tend to focus their lightning
attacks on you simultaneously, and Lightning Resistance may be your
key to survival. Lightning Enchanted Unique Monsters are considered the most deadly monsters in Diablo II, especially
with other magical bonuses such as Immunities, Teleport and Stone Skin which make them difficult to almost impossible
to kill safely. High to maximum Lightning resistance can save you against these monsters.

Fire Resistance
Fire Resistance will be very useful throughout the game, since many
monsters have Fire attacks. The Fallen Shaman, your first exposure to
Fire creatures, has an attack similar to the Sorceress' Fire Bolt
spell. Some Unique monsters are Fire Enchanted -- they have Fire
damage added to their attacks, and when they are killed, they
explode in a burst of flames, causing large amount of both Fire and
Physical damage in a small radius near them. Blood Raven may
shoot Fire Arrows. The Countess for example is
always Fire Enchanted. The Vampires from Acts II and III
(and sometimes seen in the Monastery) cast Fire Ball, Fire Wall, and
Meteor (especially in the Arcane Sanctuary). Some Frogs in Act III
also cast Fire Ball. Demon Imps in Act V have a Fire based attack and
cast Inferno from either a Barricaded Tower or Siege Beast.

Poison Resistance
Poison might just be the most annoying attack, save being Frozen. When you're poisoned, both you and
your Life Orb will turn green, and the poison will slowly drain your Hit Points. Some poisons do more damage than others,
and some have longer durations. Quite a few monsters have poison attacks: Bone Ash, found
in the Cathedral in Act I; Poison Skeletal Mages, Andariel, and the mummies in Act II; Poisonous Frogs; Swamp Monsters;
and mummies, who leave poisonous clouds behind when they die. Booby traps and trapped chests can also launch poison missiles
or leave behind poisonous clouds. Catapults in Act V sometimes have a Poison attack.
Poison can be cured instantly with an Antidote Potion. Certain magical items can reduce how long you are poisoned or how much damage Poison attacks do to you.

Melee characters are often more susceptible to Poison Attacks than ranged attackers. Mummies, Ghouls, and other monsters shoot
Poison at close range. Ghouls also leave a poisonous cloud behind when they die. Ranged attackers can avoid these attacks
more easily than melee characters.

Cold Resistance
Cold-Enchanted Unique monsters are the most likely to inflict Cold
damage. Other monsters with Cold attacks include Claw Vipers, found in
Act II, Mages with Cold melee attacks and the Summoner, who casts
Glacial Spike. The Zakarum Priests found in the jungle city of
Kurast also cast Blizzard. The Cold attack of the Undead Horrors is by
far the most damaging. It might be worth maximizing out your Cold
Resistance for that reason alone.

When they die, certain Cold-Enchanted monsters will trigger an explosive Frost Nova. Keep a Thawing Potion in your
inventory to thaw yourself instantly if you are chilled. When chilled, you move and attack much more slowly, which isn't good
for much more than a cheap laugh.

The magical ability "Half Freeze Duration" halves chill length, but
this reduction is only applied once, multiple items with this ability
do not lower chill length further, while "Cannot be Frozen"
provides the ultimate protection against chill by setting the
duration to 0. This should not be mistaken with Holy Freeze. Holy Freeze
will slow Animation speed directly while still showing the same blue overlay
as when you're chilled.

Magic Resistance
Even though it does not appear on the Character Screen, each character
has a Magic Resistance. The base is 0 for Normal, Nightmare, and Hell
difficulties. The only item that can adjust this Resistance is a
Crafted Safety Shield with +5 - 10% Magic Resistance. No skill or item
can lower Magic Resistance. The Runeword Oath can also modify the amount
of damage taken through absorption. Read below for detailed information
on absorption.

Physical Resistance
While it isn't displayed on the Character Screen either, this
Resistance reduces Physical damage just like the Elemental Resistances
lower or increase Elemental damage. On items it is displayed as
"Damage Taken Reduced by x%", and Amplify Damage lowers this by 100%,
Decrepify by 50%. It is then lower capped at -100% and upper capped at
50%.

How do items of Absorption work?
After Straight Magical Damage
Reduce and Resistances modified the damage done Absorb first heals a
player/hireling, then reduces the damage done. Since it heals first,
the double reduction rule only counts when a player or hireling is not
at full life. A drawback is that if one would end up with a negative
amount of life after resistances, you will die before Absorb reduces
the damage done.

Absorb is perfect for swarms of Imps or Fallen Shaman, but be careful
with Fire Enchanted bosses which may deal enough damage to kill you
outright. Below are a few numeric examples where 1000 fire
damage is taken. Note that the amount of damage reduced is twice
the Absorb% times the damage because half is to nullify the damage
taken, and the other half is the healing absorption provides. Note:
there is a 40% cap on absorption.

Examples
Direct absorb was not tallied in the examples below, it is usually
listed on items like this: "+x Fire Absorb" x being an integer.
The Direct Absorb would be calculated after the resistance and
percentage absorb in these next cases. (note: Heal amount of 0 = full
health upon damage taken or no absorb is present)